Process for polymerization of water-soluble and water-insoluble carboxylic acid polymers and copolymers in a silicone oil solvent

ABSTRACT

The present invention is directed to an improved process for producing water-soluble and water-insoluble carboxylic acid polymers and copolymers. The process comprises the steps of polymerizing a carboxylic acid monomer, and a polyfunctional cross-linker monomer in a second embodiment, in an effective molar ratio, in a silicone solvent under an inert atmosphere in the presence of an effective amount of an initiator. The preferred copolymer of the second embodiment includes acrylic acid as the carboxylic acid monomer and a lauryl methacrylate and/or stearyl methacrylate as a comonomer. The resulting copolymers have new and unexpected tolerance to salt-containing water when mixed therewith.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.08/327,580 filed Oct. 24, 1994, abandoned.

FIELD OF THE INVENTION

The present invention is directed to an improved process for producingcarboxylic acid polymers and copolymers in a silicone oil solvent. Thecross-linked, water-insoluble polymers and copolymers produced by theprocess of the present invention provide a viscosity that is equal to orgreater than 50,000 centipoises ("cps") when measured in water at a 0.5%by weight concentration, suited for use in foods, cosmetics, printinginks, pastes, and coating applications. The cross-linked,water-insoluble copolymers produced from acrylic acid and the fattyesters (C₈ -C₃₀) of α,β unsaturated acids, such as acrylic acid and/ormaleic acid, e.g., lauryl methacrylate and stearyl methacrylate, areparticularly resistant to salt-containing water, for viscosifying andabsorption of saline-containing water, urine, and the like.

BACKGROUND OF THE INVENTION

Others have produced non-cross-linked polyacrylates for use as drillingfluid additives, as disclosed in U.S. Pat. Nos. 4,709,767 and 4,794,140,from an aqueous solution of partially neutralized acrylic acid.

Also, numerous processes are known in the art for producingcross-linked, water insoluble, viscosifying acrylic polymers. Forexample, EPO Publication No. 0 371 421 A2 discloses a process forproducing a cross-linked polyacrylic acid polymer in a solvent selectedfrom acetone, alkyl acetates, and mixtures thereof. One problem with the'421 process is that it uses the organic solvent ethyl acetate, oracetone, either of which is flammable, hazardous, and requires specialhandling provisions. A second problem with the process of the '421disclosure is that the best polymer that was capable of being producedby the disclosed process only had a viscosity of 59,200 cps for a 1%solution.

U.S. Pat. No. 3,915,921 to Schlatzer, which issued on Oct. 28, 1975,discloses a viscosifying copolymer that is produced by copolymerizing acarboxylic acid monomer and one or more alkyl acrylate esters. The '921patent, like the previously discussed '421 patent, disclosescopolymerization that occurs in an organic solvent such as benzene,xylene, tetralin, heptane, hexane, carbon tetrachloride, methylchloride,ethylchloride, bromotrichloromethane, dimethylcarbonate,diethylcarbonate, ethylenedichloride, and mixtures thereof. Thus, aproblem with the '921 process, like that of the '421 process, is that itutilizes hydrocarbon solvents, which are flammable and in many instanceshazardous to health, while the halocarbon solvents are generally justhazardous. Polymerization in any one of the disclosed solvents can giverise to hazardous and/or flammable vapor emissions, which requirespecial precautions. A second problem with the Process disclosed in the'921 patent is that the best viscosity that was reported for any polymerat the 0.5% by weight concentration in water was 71,200 cps.

U.S. Pat. No. 4,509,949 to Huang, which issued on Apr. 9, 1985,discloses a process for producing water thickening agents consisting ofcopolymers of acrylic acids and esters that are cross-linked with apolyfunctional vinylidene monomer containing at least two terminal CH₂groups. One problem with the '949 process, like most of the processes ofthe prior art, is that the '949 process also teaches polymerization in agenerally hazardous solvent such as "benzene, tetralin, hexane, heptane,cyclohexane, carbontetrachloride, chloroform, trichloroethylene,methylchloride, ethylchloride, and methylenechloride;chlorofluoroalkanes, such as chlorofluoromethane and chlorofluoroethane,each containing at least four halogen atoms; esters such asmethylacetate and ethylacetate, alcohols including methanol, ethanol,butanol and the like." ['949 at column 4, lines 37-44.] Another problemwith the '949 process is that it is only capable of producing polymersthat at best provide modest increases in viscosity. For example, thebest viscosity that was produced by the products of the '949 process was12,000 cps for a 1.2% by weight solution of the polymer. ['949 at column8, line 8.]

In view of the problems commonly associated with the '421, '921 and '949patents, it is an object of the present invention to produce awater-soluble acrylic polymer or a cross-linked, water-insoluble,acrylic viscosifying polymer in a non-hazardous and a non-flammablesolvent that generally does not require special handling. In addition,an object of one embodiment of the present invention is that thecross-linked, water-insoluble polymer produced by the process of thepresent invention has a viscosity of at least 50,000 cps when measuredas a 0.5% by weight solution in water at room temperature.

One method for producing a viscosifying polymer that does not usehydrocarbon or halocarbon solvents is disclosed in EPO Publication No. 0301 532 A2, which was published on Feb. 1, 1989. The '532 disclosureteaches that copolymerization can be effected in carbon dioxide to yielda fluffy powder when the acrylic acid, the comonomer, and the chemicalinitiator are dissolved in a single liquid phase, i.e., liquid carbondioxide. The best viscosity that was obtained with the product producedby the '532 process was 12,550 cps for 0.2% by weight solution in water.One problem with the '532 process is that the carbon dioxide must bepressurized in order to form a liquid at the reaction temperatures. Inparticular, pressures of 1200 to 2500 pounds per square inch would notbe uncommon. Such pressurized reactions require special reaction vesselsand equipment. An object of the present invention is to provide aprocess for producing a viscosifying polymer that is capable ofutilizing a conventional, unpressurized reactor.

A second problem with the '532 process is that it produces a producthaving a low viscosity (12,550 cps for a 0.2% by weight solution). Toovercome such low viscosities, an object of one embodiment of thepresent invention is to provides a process that produces a viscosifyingcopolymer that exhibits a viscosity of 50,000 cps or greater in a 0.5%by weight aqueous solution.

SUMMARY OF THE INVENTION

The present invention has two embodiments. In a first embodiment of thepresent invention, a water-soluble acrylic polymer or copolymer ismanufactured by polymerizing a carboxylic acid monomer, preferably anacrylic monomer, without using a cross-linking agent, in a siliconesolvent, under an inert atmosphere in the presence of an effectiveamount of a polymerization initiator. In its second embodiment, thepresent invention is directed to an improved process for manufacturing awater-insoluble, cross-linked viscosifying polymer or copolymer. Theprocess of the second embodiment of the present invention includes thesteps of polymerizing a carboxylic acid monomer, preferably an acrylicmonomer, and a cross-linker monomer, in a molar ratio of 1:0.03 to1:0.10, respectively, in a silicone solvent, under an inert atmospherein the presence of an effective amount of an initiator to form aviscosifying polymer that a 0.5% by weight aqueous mucilage provides aviscosity of about 50,000 to 300,000 cps. A preferred initiator for bothembodiments of the process of the present invention is a redox system.

In the second embodiment of the present invention, the process isdirected to the manufacture of a viscosifying polymer or copolymercomprising a cross-linked polymer polymerized from one or morecarboxylic acid monomers and a polyfunctional cross-linking agent in amolar ratio of about 1:0.03 to 1:0.10, respectively. The viscosifyingcopolymer of the second embodiment of the present invention ischaracterized in that a 0.5% by weight aqueous solution of theviscosifying copolymer has a viscosity of about 50,000 to about 300,000cps, preferably about 100,000 to 300,000 cps, and more preferably, about200,000 to about 300,000 cps.

DETAILED DESCRIPTION OF THE INVENTION

The present invention has multiple aspects. In a first aspect, thepresent invention is directed to an improved process for producing awater-soluble carboxylic acid polymer or copolymer in a silicone oilsolvent. In accordance with another aspect of the present invention, animproved process is directed to manufacturing a water-insoluble,cross-linked carboxylic acid polymer or copolymer capable of providingnew and unexpected increases in viscosity to aqueous solutions orsuspensions. The process of manufacturing the cross-linked,water-insoluble polymers and copolymers of the present inventioncomprises the steps of:

Polymerizing a carboxylic acid monomer and a polyfunctional cross-linkermonomer in a molar ratio of about 1:0.03 to 1:0.10, respectively, in asilicone solvent under an inert atmosphere in the presence of aneffective amount of initiator to form a viscosifying polymercharacterized by being capable of producing a 0.5% by weight aqueousmucilage that has a viscosity of about 50,000 to 300,000 cps. Allviscosities referenced herein are measured on a Brookfield Viscometerusing ASTM E-2196 at 1 RPM.

Where the carboxylic acid monomer is acrylic acid and the cross-linkermonomer is a bifunctional cross-linker such as allyl methacrylate, theeffective molar ratio between the acrylic acid and the allylmethacrylate is 1:0.03 to 1:0.10. As the functionality of thecross-linker monomer increases, from bifunctionality totrifunctionality, tetrafunctionality and multifunctionality, the amountof cross-linker monomer that is needed to provide an "effective molarratio" decreases due to the increasing equivalency of each molecule ofcross-linker.

The process of the present invention utilizes a carboxylic acid monomeri.e., a carboxylic acid having at least one unsaturated carbon-carbondouble bond. Suitable carboxylic acid monomers include theolefinically-unsaturated carboxylic acids containing at least onecarbon-to-carbon olefinic double bond, and at least one carboxyl groupwhich readily functions in polymerization because of its presence in themonomer molecule, either in the alpha-beta position with respect to acarboxyl group, --C═C--COOH; or as part of a terminal methylenegrouping, CH₂ ═C<. Olefinically-unsaturated acids of this class includesuch materials at the acrylic acids; alpha-cyano acrylic acid; betamethylacrylic acid (crotonic acid); alpha-phenyl acrylic acid,beta-acryloxy propionic acid; cinnamic acid; p-chloro cinnamic acid;1-carboxy-4-phenyl butadiene-1,3, itaconic acids; citraconic acid;mesaconic acid; glutaconic acid; aconitic acid; maleic acid; fumaricacid; and tricarboxy ethylene. As used herein, the term "carboxylicacid" includes the polycarboxylic acids and those acid anhydrides, suchas maleic anhydride, wherein the anhydride group is formed by theelimination of one molecule of water from two carboxyl groups located onthe same carboxylic acid molecule. Maleic anhydride and other acidanhydrides useful herein have the general structure ##STR1## wherein Rand R' are selected from the group consisting of hydrogen, halogen andcyanogen (--C.tbd.N) groups and alkyl, aryl, alkaryl, aralkyl, andcycloalkyl groups such as methyl, ethyl, propyl, octyl, decyl, phenyl,tolyl, xylyl, benzyl, cyclohexyl, and the like.

The preferred carboxylic monomers are the monolefinic acrylic acidshaving the general structure ##STR2## wherein R² is a substituentselected from the class consisting of hydrogen, halogen, and thecyanogen (--C.tbd.N) groups, monovalent alkyl radicals, monovalent arylradicals, monovalent aralkyl radicals, monovalent alkaryl radicals andmonovalent cycloaliphatic radicals. Of this class, acrylic andmethacrylic acid are most preferred. Other useful carboxylic monomersare maleic acid and its anhydride.

The polymers manufactured in accordance with the present inventionincludes both homopolymers of carboxylic acids or anhydrides thereof, orthe defined carboxylic acids copolymerized with one or more othermonomers containing at least one terminal >CH₂ group. Such monomersinclude, for example, acrylate ester monomers including those acrylicacid ester monomers such as derivatives of an acrylic acid representedby the formula ##STR3## wherein R³ is an alkyl group having from 1 to 30carbon atoms, preferably 1 to 20 carbon atoms and R₂ is hydrogen, methylor ethyl, present in the copolymer in an amount, for example, from about1 to 40 weight percent or more. Representative acrylates include methylacrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butylacrylate, isobutyl acrylate, methyl methacrylate, methylα-ethyl-acrylate, ethyl methacrylate, octyl acrylate, heptyl acrylate,octyl methacrylate, isopropyl methacrylate, 2-ethylhexyl methacrylate,nonyl acrylate, hexyl acrylate, n-hexyl methacrylate, and the like.Higher alkyl acrylic esters are decyl acrylate, isodecyl methacrylate,lauryl acrylate, stearyl acrylate, behenyl acrylate and melissylacrylate. Mixtures of two or three or more long chain acrylic esters maybe successfully polymerized with one of the carboxylic monomers. Othercomonomers include olefins, including alpha olefins, vinyl ethers, vinylesters, and mixtures thereof. A preferred carboxylic acid monomer is"acrylic acid." By the term "acrylic acid" as used herein is meantacrylic acid and its homologs such as methacrylic acid, α-ethyl-acrylicacid, itaconic acids, maleic acids and their respective anhydrides.

The second embodiment of the process of the present invention utilizes apolyfunctional cross-linker monomer, i.e., a monomer having at least twounsaturated carbon-carbon double bonds, each of which is capable ofpolymerizing independently of the other. Typical cross-linker monomersare bifunctional, trifunctional or tetrafunctional monomers.Representative bifunctional monomers include allyl methacrylate, allylacrylate, dimethyldiallyl ether, divinyl benzene, bisphenol Adimethacrylate, divinyl glycol and ethylene glycol dimethacrylate.Typical trifunctional cross-linkers include triallyl isocyanurate,triallylcyanurate, trimethylolpropane triacrylate, trimethylolpropanetrimethacrylate. Typical tetrafunctional cross-linker monomers includetetramethylolmethane tetraacrylate, tetramethylolmethanetetramethacrylate and tetravinyl silane. Typical polyfunctionalcross-linker monomers include allyl pentaerythritol, trimethylolpropanediallyl ether and allyl sucrose. Other cross-linking monomers include,for example, diallyl esters, dimethallyl esters; allyl or methallylacrylates and acrylamides; tetraallyl tin; tetravinyl silane;polyalkenyl methanes; diacrylates, and dimethacrylates; divinylcompounds such as divinyl benzene; polyallyl phosphate; diallyloxycompounds; phosphite esters and the like. Typical agents are allylpentaerythritol; allyl sucrose; trimethylolpropane triacrylate;1,6-hexanediol diacrylate; trimethylolpropane diallyl ether;pentacrythritol triacrylate; tetramethylene dimethacrylate; ethylenediacrylate; ethylene dimethacrylate; triethylene glycol dimethacrylate;and the like. Allyl pentaerythritol; trimethylolpropane diallylether;and allyl sucrose provide excellent polymers. When the cross-linkingagent is present, the polymeric mixtures usually contain up to about 5%or more by weight of cross-linking monomer, based on the total ofcarboxylic acid monomer, plus other monomers, if present, and morepreferably about 0.01 to 3.0 weight percent.

In the improved process of the present invention, the copolymerizationis achieved under an inert atmosphere. Typically, the inert atmosphereis provided by bubbling or flushing nitrogen, carbon dioxide or argoninto the reaction mixture. Although other non-reactive gases may beused, the preferred inert gases are nitrogen and/or argon.Polymerization of the carboxyl-containing monomers, optionally withother comonomers, is usually carried out in the presence of a freeradical catalyst in a closed vessel in an inert atmosphere or in an openvessel in an inert atmosphere optionally under reflux at atmosphericpressure. The temperature of the polymerization may be varied from about0° C. to 125° C. or lower or higher. Polymerization at 25° C. to 90° C.using a free radical catalyst is generally effective in providingmonomer to polymer conversion of 75% to 100%.

The polymerization of the improved process of both embodiments of thepresent invention is performed in a silicone solvent. As shown inExample 4, herein, polymerization of water-insoluble, cross-linkedpolymers and copolymers, performed in accordance with the presentinvention in a silicone solvent, are capable of producing a viscosifyingcopolymer that has a significantly greater viscosity than that producedby the identical polymerization reaction that is carried out in ahydrocarbon solvent, such as ethylacetate, or water. Typical siliconesolvents for use in the improved process of the present invention arethe cyclomethicones, the linear polydimethylsiloxanes, the aromaticphenyl-containing siloxanes, the polymethylalkyl siloxanes and thefluorosilicones, which are commercially available from a variety ofsources, including Dow Corning, Midland, Mich., General ElectricCompany, Walker and Goldschmidt, Huls, or Petrarch.

By way of example, the cyclomethicone solvents which are within thescope of the process of the present invention includehexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane,decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane and mixturesthereof.

By way of further example, the linear polydimethyl siloxane solvents,which are useful in the process of the present invention, are of theformula: (CH₃)SiO[SiO(CH₃)₂ ]_(x) Si(CH₃)₃ wherein x=0.65-2,500,000, andincludes hexamethyl disiloxane (i.e., x=0), octamethyl trisiloxane(i.e., x=1), decamethyl tetrasiloxane (i.e., x=2), dodecamethylpentasiloxane (i.e., x=3), etc. and mixtures thereof. The linearpolydimethyl siloxane solvents that are used in the process of thepresent invention are typically non-volatile with boiling points over192° C., and are represented by the above formula whereinx=1.5-2,500,000. More typically, the linear polydimethyl siloxanesolvents that are used in the process of the present invention are ofthe above formula wherein x=1.5-100; most typically, x=1.5-10.

The aromatic phenyl-containing siloxanes include the diphenyl dimethylsiloxane copolymers and the phenylmethyl siloxane polymers which are ofthe Formulas I and II below, respectively: ##STR4## wherein "m" and "n"may be the same or different and are each an integer from 1-100. Mosttypically, "m" and "n" are separately an integer from 1-10. Otheraromatic phenyl-containing siloxanes include1,1,5,5-tetraphenyl-1,3,3,5-tetramethyltrisiloxane, and1,1,3,5,5-pentaphenyl-1,3,5-trimethyl trisiloxane.

The polymethylalkyl siloxane solvents are of the formula: ##STR5##wherein p and q are integers from 1-100 and 1-30, respectively.

Typical fluorosilicones are the polyfluoroalkyl methyl siloxanes, whichare of the formula: ##STR6## wherein r is an integer from 1-100.

It is also within the scope of the improved process of the presentinvention that the silicone solvent includes mixtures of one or more ofthe silicone solvents disclosed herein.

Both embodiments of the process of the present invention also utilizesan effective amount of an initiator. By "effective amount of aninitiator" is meant the amount of initiator that is effective tomanufacture a polymer or copolymer that, in the water-solubleembodiment, provides a water-soluble polymer or copolymer having aweight average molecular weight in the range of about 1,000 to about5,000,000, typically about 3,000 to about 1,000,000, and iswater-soluble. Such water-soluble polymers may be slightly cross-linkedso long as the polymer remains water-soluble (herein defined as capableof solubilizing at least 5 grams out of 100 grams when stirred in 1liter of water at 25° C.). An "effective amount of initiator" for thesecond embodiment of the present invention, in the manufacture of thecross-linked, water-insoluble carboxylic acid polymers and copolymers,is meant the amount of initiator that is effective to manufacture awater-insoluble polymer or copolymer that in a 0.5% by weight aqueousmucilage, is capable of providing a viscosity of at least 50,000 cps asmeasured using ASTM E-2196 at 1 RPM. To determine an effective amount ofinitiator, one of ordinary skill in the art would begin with a smallamount of initiator and then increase the amount of initiator until thedesired degree of polymerization, and cross-linking for the secondembodiment, is obtained. Typically, an effective amount of initiator isfrom about 0.01 mole percent to 5 mole percent, wherein by the term"mole percent" is meant the percentage of the initiator, relative to allpolymerizable reactants, as measured in moles.

Initiators that are suitable for use in both embodiments of the presentinvention are, for example, the peroxide, azo, amino or nitrile type.Suitable initiators of the peroxide type include the organic peroxides,such as t-butyl hydroperoxide, cumene hydroperoxide and dibenzoylperoxide. The organic peroxides are commercially available from sourcessuch as Aztec Peroxides Inc., Elyria, Ohio. Suitable inorganic peroxideinitiators include hydrogen peroxide, the water-soluble per-acids, andtheir salts. The water-soluble per-acid salts include the alkali-metalor ammonium persulfates, perphosphates, perborates, perchlorates,percarbonates, and the like, such as sodium or potassium perphosphate,potassium percarbonate, sodium perchlorate, sodium perborate, ammoniumperborate and the like.

The organic peroxycarbonates and -dicarbonates also are useful asinitiators in accordance with both embodiments of the present invention.Suitable peroxycarbonates and -dicarbonates include the following:t-butylperoxy 2-ethylhexyl carbonate; di(4-t-butylcyclohexyl)peroxydicarbonate, dimyristyl peroxydicarbonate; and dicetylperoxydicarbonate, all of which are commercially available in an aqueoussuspension, for example, from Aztec Peroxides, Inc., Elyria, Ohio.

Other polymerization initiators that are capable of being used in bothembodiments of the present invention are the easily decomposable organic"azo" compounds, such as2,2'-azobis(2-methylpropanamidine)dihydrochloride;2,2'-azobisisobutyronitrile; 2,2'-azobis(2,4-dimethylpentanenitrile);2,2'-azobis(2-methylbutanenitrile);1,1'-azobis(cyclohexanecarbonitrile); and 2,2'-azobis(isobutyronitrile).Many of the azo compounds are available from DuPont, Wilmington, Del.under the VAZO® tradename.

A particularly preferred polymerization initiator for use in bothembodiments of the process of the present invention is a redoxcouple/multiple system. A "redox couple/multiple system" is acombination of one or more oxidizing agents and one or more reducingagents that generate transient free radicals during the course of theredox reaction. In many instances, the oxidizing agent is an inorganicor organic peroxide. The reducing agent is any one or more of a varietyof reducing agents, alone or in combination with one or more activators.For example, when the oxidizing agent is hydrogen peroxide and thereducing agent is Fe⁺² (a redox couple system) suitable activatorsinclude ammonia, aliphatic amines, Na₂ S₂ O₃, thiourea, ascorbic acid,glyoxal, sodium nitrite or hydroxylamine.

When the oxidizing agent is an organic peroxide, suitable reducingagents include sulfonic acids, α-ketals, formic acid, thiols, andtertiary amines alone or in combination with a soluble metal ionenhancing agent (i.e., salts of Pb, Fe, Co, Ni, Mn, Cu, Zn, or Ce)and/or an activator, such as NaHSO₃ mercaptans, diphenylthiourea,ascorbic acid, and the azobisnitriles.

A preferred redox couple/multiple system is a mixture of a peroxide andan azo compound. Preferably, the peroxide and the azo compound arepresent in the mixture in a 1:1 molar ratio. A particularly preferredredox couple/multiple system for use in the present invention is thecombination of dibenzoyl peroxide and2,2'-azobis(2,4-dimethylpentanenitrile) at about a 1:1 molar ratio.Regardless of the initiator selected, the process of the presentinvention requires an effective amount of an initiator to form thepolymers and copolymers of both embodiments of the present invention.

It has been found, unexpectedly, that when allyl methacrylate is thepolyvalent cross-linker monomer in the process of the second embodimentof the present invention, to manufacture a water-insoluble polymer orcopolymer, a viscosifying polymer is produced that is characterized byits ability to produce high viscosities even in a 0.5% by weight aqueousmucilage. As reflected in Example 5, when a molar equivalent of allylmethacrylate cross-linker is used in the second embodiment of theprocess of the present invention, a 0.5% aqueous mucilage of theresulting copolymer has a viscosity of about 143,000 cps whereas, whenallyl acrylate is substituted for allyl methacrylate in the secondembodiment of the process of the present invention, a 0.5% aqueousmucilage of the resulting copolymer in an aqueous solution is onlycapable of producing a viscosity of about 27,500 cps.

In the second embodiment of the process of the present invention themolar ratio of acrylic acid to allyl methacrylate is about 1:0.03 to1:0.1, respectively. Preferably, the molar ratio of acrylic acid toallyl methacrylate is 1:0.03 to 1:0.09, respectively. This is reflectedin Table II of Example 5, wherein when lauroyl peroxide was theinitiator, a molar ratio of acrylic acid to allyl methacrylate in therange of 1:0.03 to 1:0.09 produced a viscosifying copolymer that wascharacterized by a viscosity of at least 72,000 cps, i.e., within therange of 72,000 cps to 143,000 cps.

A more preferred molar ratio of acrylic acid to allyl methacrylate is1:0.06 to 1:0.08, respectively.

The process of the second embodiment of the present invention is capableof producing viscosifying polymer that is characterized by its abilityto produce highly viscous solutions even when present in lowconcentrations. In particular, the second embodiment of the process ofthe present invention produces a water-insoluble, viscosifying polymeror copolymer that at 0.5% by weight in water provides a mucilage havinga viscosity of about 50,000 to about 300,000 cps; preferably, about100,000 to about 300,000 cps; more preferably, about 200,000 to about300,000 cps.

In the water-insoluble, viscosifying copolymer of the second embodimentof the present invention, the preferred molar ratio of the preferredreactants, acrylic acid to allyl methacrylate, is about 0.06 to 1:0.08.

EXAMPLE 1

Into a 2000 ml three neck flask equipped with a stirrer, thermometer,and condenser was added'324.00 grams of Dow Corning® 244, i.e.,octamethylcyclotetrasiloxane, and the siloxane was purged with argon. Ina beaker, and during an argon gas purge of the silicone solvent, 36.00grams of acrylic acid were pre-neutralized with 0.518 grams of anhydrouspotassium carbonate by mixing potassium carbonate in acrylic acid untilthe potassium carbonate dissolved which took about one-quarter of anhour. To the beaker was added 0.44 grams allyl methacrylatecross-linker, and 0.144 grams lauroyl peroxide and the mixture wasstirred for five minutes. The contents of the beaker were then pouredinto the reactor containing the Dow Corning® 244 and stirred at 100 rpmuntil it became clear, which took about one-half of an hour. With theinert purge continuing at the top of the reactor, heating was commencedat room temperature, T 22° C. When the reaction mixture was about 44° C.the first spot of a polymer was detected visually, and heating wascontinued to 70° C., whereupon the external heating was discontinued andthe exothermic reaction was allowed to proceed on its own. At 78° C.,the entire contents of the reaction flask became slightly hazy. At 85°C., the contents were white in color. The exothermic reaction attained amaximum temperature of 122° C. After cessation of the exotherm, thesystem was allowed to cool to 90° C. at which time mild heating wasemployed, and a temperature of 90° C. was maintained for five hours. Thepolymer was recovered from the reaction flask and filtered to removeremaining silicone solvent. The polymer was then dried in an oven fortwelve hours at 60° C. The dry polymer was particulate and free-flowingwith an average aggregate particle size of 20 microns and the viscosityof a 0.5% by weight mucilage as measured on a Brookfield viscometer,using ASTM E-2196, was 143,000 cps at pH 7, 1 RPM. When measured at 1RPM and 0.5 RPM, the yield value of viscosity was 379.

EXAMPLE 2

The polymers of Example 2 were prepared according to the process ofExample 1 with the exception that the initiator of Example 1 wasreplaced by the various initiators of Example 2.

Example 2 demonstrates the use of different chemical initiators: t-butylperoctoate, Vazo 52, Vazo 64, redox dibenzoyl peroxide/Vazo 52, anddibenzoyl peroxide, in the process of the present invention. Thecopolymers produced showed significant differences in thickeningefficiency. The abbreviations used in Tables I and II are identified asfollows:

AMA--allyl methacrylate

ALA--allyl acrylate

DVB--divinyl benzene

BADM--bisphenol A dimethacrylate

EGDM--ethylene glycol dimethacrylate

DVG--divinyl glycol

TMPTMD--trimethylolpropane trimethacrylate

TVS--tetravinyl silane

t-BPO--t-butyl peroctoate

DBP--dibenzoyl peroxide

Vazo 52--2,2'-azobis(2,4-dimethylpentanenitrile)

Vazo 64--2,2'-(2-methylpropanenitrile)

APE--allyl pentaerythritol

TMPDAE--trimethylolpropane diallylether

                  TABLE I                                                         ______________________________________                                        Mono-                               Mucilage                                  mer                                 Viscosity                                 AA     Cross-linker Initiator       (cps)                                     WT %   Type    Mole %   Type    Mole %  0.5%                                  ______________________________________                                        10     AMA     0.07     t-BPO   0.05    101,000                               10     AMA     0.07     Vazo 52 0.02     51,000                               10     AMA     0.07     Vazo 64 0.03     48,000                               10     AMA     0.07     DBP/Nazo                                                                              0.015/0.015                                                                           244,000                                                       52                                                    10     AMA     0.07     DBP      0.045  100,300                               ______________________________________                                    

EXAMPLE 3

Employing the procedure and the equipment of Example 1, a series ofacrylic acid-allyl methacrylate copolymers was made inpolydimethylcyclosiloxanes such as Dow Corning® 244, Dow Corning® 344,Dow Corning® 245, Dow Corning® 345 and linear polydimethylsiloxanes suchas 200® fluids. Dow Corning® 244 (D4) is octamethylcyclotetrasiloxane,b.p. 172° C. Dow Corning® (D5) is decamethylcyclopentasiloxane, b.p.205° C. Dow Corning® 344 is a mixture of D4/D5 90/10%, b.p. 178° C. DowCorning® 345 is a mixture of D5/D6, b.p. 217° C., wherein D6 isdodecamethylcyclohexasiloxane. All are in the category ofcyclomethicones. The 200® fluids are linear polydimethylsiloxanes (alsoknown as dimethicones). Only two of them are volatile: the 200® fluid0.65 cs, which is hexamethyldisiloxane (b.p. 100° C.) having the formula(CH₃)₃ SiOSi(CH₃)₃ ; and 200® fluid 1.0 cs, which isoctamethyltrisiloxane b.p. 152° C., has the formula (CH₃)₃ SiO(CH₃)₂SiOSi(CH₃)₃. Other 200® fluids are non volatile with boiling points over192° C. and their typical chemical composition is (CH₃)₃ SiO[SiO(CH₃)₂]_(x) Si(CH₃)₃ (where x=1 to 2,500,000). In each instance, a viscosityover 40,000 cps was obtained for a 0.5% mucilage neutralized to pH 7 andmeasured at 1 RPM using ASTM E-2196.

EXAMPLE 4

Example 1 was repeated except that concentration of acrylic acid in thesolvent was changed from 10% by weight to 8% by weight. The resultingpolymer provided a viscosity of 178,000 cps at 0.5% by weight mucilageas measured on a Brookfield Viscometer using ASTM E-2196 at 1 RPM.

EXAMPLE 5

A number of polymers were produced in accordance with the typicalprocess as it has been described in Example 1, except that differentcross-linkers were employed. The viscosities of their respective 0.5% byweight mucilages were measured on a Brookfield viscometer using ASTME-2196 at 1 RPM. The results are reported in Table II.

                  TABLE II                                                        ______________________________________                                                        MUCILAGE                                                      CROSS-LINKER      VISCOSITY (cps)                                             Type         Mole %   0.5%                                                    ______________________________________                                        ALA          0.07     27,500                                                  DVB          0.07      2,000                                                  BADMA        0.07       300                                                   EGDMA        0.07       300                                                   DVG          0.07       300                                                   AMA          0.01     11,500                                                  AMA          0.03     72,000                                                  AMA          0.05     95,400                                                  AMA          0.07     143,000                                                 AMA          0.09     109,000                                                 AMA          0.11     39,000                                                  TMPTMA       0.07      4,900                                                  TVS          0.07     17,200                                                  APE          0.02     128,000                                                 TMPDA        0.05     127,000                                                 ______________________________________                                    

EXAMPLE 6

This example is set forth for purposes of comparison. Following theprocedure of Example 1, polymerization was run substituting ethylacetate as the solvent in place of Dow Corning® 244. The copolymer thatwas produced in the ethyl acetate exhibited a viscosity of 103,000 cpsviscosity at 0.5% by weight mucilage, whereas the copolymer of Example1, that was identically produced but for being polymerized in a siloxanesolvent, exhibited a viscosity of 143,000 cps (ASTM E-2196 at 1 RPM) at0.5% by weight mucilage.

EXAMPLE 7

In a 2 liter glass reactor equipped with a stirrer, a thermometer and areflux condenser, 263 grams of the Dow Corning® 244 silicone solventwere placed along with 0.15 grams of Vazo 52 initiator. The mixture wasagitated at 60 RPM for half an hour and purged with argon for the sametime. Separately, in an addition funnel, 47 grams of acrylic acid werepurged with argon for 15-20 minutes. Purging of contents in the reactorand the addition funnel was ceased after elapse of the time. With theinert purge continuing at the top of the reactor, heating was commenced.When the reaction mixture reached 70° C., metering of acrylic acid wasstarted at the rate of 0.281 gram/min. Polymerization was evident byformation of turbidity at 72° C. During polymerization, viscosity of theslurry was enhanced. In order to keep uniform mixing, revolution wasadjusted to 100 RPM. Metering was finished at a constant rate at 3hours. The slurry was recovered from the reaction flask and filtered toremove the remaining silicone solvent. The polymer was then dried in anoven at 80° C. The dry polymer was particulate and free flowing.Molecular weight of the polymer was 700,000. The polymer was easy todissolve in water to a crystal clear solution.

EXAMPLE 8

The polymer of Example 8 was prepared according to the process ofExample 7 with the exception that 3 - mercaptopropionic acid at levelsof 1-5 mole percent, based on acrylic acid, as a chain transfer agent,was employed in the synthesis. The data are set forth in Table III.

                  TABLE III                                                       ______________________________________                                        Chain                   Weight Average                                        Transfer Agent                                                                           Mole % of AAA                                                                              Molecular Weight, Mw                                  ______________________________________                                         3-MPA*    1            27,000                                                3-MPA      2            21,000                                                3-MPA      3            7,000                                                 3-MPA      4            5,000                                                 3-MPA      5            4,000                                                 ______________________________________                                         *3-MPA = 3mercaptopropionic acid                                         

EXAMPLE 9

Polymerization was conducted in a 2 liter round bottom three neck flask,equipped with stirrer, thermometer, condenser and nitrogen purge. Thesilicone solvent Dow Corning® 244 (263 gs) was initially charged intothe reactor flask and purged with oxygen free nitrogen. The appropriateamounts of comonomer (see Table IV) and 0.04 grams allylmethacrylatecross-linker were dissolved in 36 grams of acrylic acid, which was thenpre-neutralized with 0.518 grams of potassium carbonate, while anitrogen purge was employed. The monomer mixture was subsequently addedto the reaction flask containing the silicone fluid and stirring wascontinued until the reaction mixture became clear. A nitrogen purge wasmaintained throughout the mixing procedure. To the reaction mixture0.086 grams of 6-butyl percolate initiator were added and agitationdiscontinued prior to commencement of heating. Initial spots of polymerwere visible at the bottom of the reactor from a ca 50° C. The mixtureturned cloudy from ca 78° C. and a white precipitate was formed from 80°C. In order to prevent the exotherm, cooling was employed from 90° C.After cessation of the exotherm, the temperature of the reaction flaskWas maintained at 70° C. for 6 hours. The polymer recovered from theflask was filtered, to remove remaining silicone fluid and then dried inan oven at 100° C. for three hours.

                  TABLE IV                                                        ______________________________________                                                            Viscosity (cps) as                                                            measured by                                                                   Brookfield RVT                                                                viscometer 1 wt %                                                Comonomer      pH 7, 1 RPM                                             Comonomer                                                                              wt % on acrylic acid                                                                           Water   1% saline                                   ______________________________________                                        0        0                123,000 5,800                                       LM       3.5              128,000 6,000                                       SM       3.5              148,000 5,200                                       LM       6.7              224,000 5,800                                       Sm       6.7              192,000 2,000                                       ______________________________________                                         LM: Lauryl methacrylate                                                       SM: Stearyl methacrylate                                                 

EXAMPLE 10

The procedures for preparation of hydrophobically modified polyacrylicacid as described in Example 9 was repeated, except that no cross-linkerwas used. The data are set forth in Table V.

                  TABLE V                                                         ______________________________________                                                            Viscosity (cps) as                                                            measured by                                                                   Brookfield RVT                                                                viscometer 1 wt %                                                Comonomer      pH 7, 1 RPM                                             Comonomer                                                                              wt % on acrylic acid                                                                           H.sub.2 O                                                                             1% saline                                   ______________________________________                                        0        0                   160  soluble                                     LM       2.8               29,600 36,400                                      SM       2.8               17,600 46,400                                      LM       5.6               24,000 30,000                                      SM       5.6              202,000 10,800                                      LM       8.3               42,000 22,400                                      SM       8.3              252,000   500                                       LM       11.1             110,000 12,000                                      SM       11.1             314,000   600                                       ______________________________________                                         LM: Lauryl methacrylate                                                       SM: Stearyl methacrylate                                                 

Viscosities were typically measured at 1 wt % concentration usingBrookfield LVT viscometer and a spindle speed 1.5 RPM. Salt sensitivitywas determined at 1 wt % saline, the NaCl being added in solid form toneutralized microgel, while stirring. After the salt addition, sampleswere left to equilibrate for at least 2 hours before the viscosity wasmeasured. From patent literature, this would appear to be the standardprocedure for examining salt tolerance.

What is claimed is:
 1. An improved process for viscosifying metalsalt-containing aqueous media comprising the steps of:copolymerizing acarboxylic acid monomer and a polyfunctional cross-linker monomer in amole ratio of about 1:0.03 to 1:0.10, respectively, in a siliconesolvent, under an inert atmosphere, in the presence of an effectiveamount of initiator to form a metal salt-containing water-viscosifyingpolymer; and adding an effective amount of said polymer to said metalsalt-containing water.
 2. The process of claim 1, wherein the carboxylicacid monomer is selected from the group consisting of acrylic acid,neutralized acrylic acid, metal salts of acrylic acid, and mixturesthereof.
 3. The process of claim 1, wherein the initiator is a memberselected from the group consisting of a peroxide initiator and a redoxinitiator.
 4. The process Of claim 1, wherein the initiator is a redoxinitiator.
 5. The process of claim 4, wherein the redox initiatorincludes a mixture of a peroxide and an azo compound.
 6. An improvedprocess for viscosifying an inorganic metal salt-containing watercomprising adding to said salt-containing water an effective amount ofan acrylic polymer, said acrylic polymer manufactured by a processcomprising the steps of:copolymerizing an acrylic acid monomer and apolyfunctional cross-linker monomer in a mole ratio of about 1:0.03 to1:0.10, respectively, in a silicone solvent, in the presence of aneffective amount of an acrylic acid polymerization initiator to form awater-viscosifying polymer capable of viscosifying water containing aninorganic metal salt.
 7. The process of claim 6, wherein the salt isNaCl in an amount of about 0.1% to about 5% by weight of thesalt-containing water.
 8. An improved process for viscosifying aninorganic metal salt-containing water comprising adding to saidsalt-containing water an effective amount of an acrylic polymer, saidacrylic polymer manufactured by a process comprising the stepsof:copolymerizing an acrylic acid monomer, neutralized 25 to 100 molepercent, and a polyfunctional cross-linker monomer in a mole ratio ofabout 1:0.03 to 1:0.10, respectively, in a silicone solvent, under aninert atmosphere, in the presence of an effective amount of initiator toform a water-viscosifying polymer.
 9. A method of increasing theviscosity of water comprising the steps of:polymerizing a carboxylicacid monomer in a silicone solvent, under an inert atmosphere, in thepresence of an effective amount of initiator to form a carboxylic acidpolymer, capable of being dissolved in water; and adding an effectiveamount of said polymer to said water.
 10. A method of increasing theviscosity of metal salt-containing water comprising polymerizing acarboxylic acid monomer and a polyfunctional cross-linker monomer in asilicone solvent, to form a cross-linked viscosifying copolymer, saidcarboxylic acid monomer selected from the group consisting of acrylicacid, neutralized acrylic acid, C₈ -C₃₀ esters of acrylic acid, C₈ -C₃₀esters of methacrylic acids, and mixtures thereof, wherein saidcarboxylic acid monomer and said polyfunctional cross-linker monomer arepresent at a mole ratio of 1:0.03 to 1:0.1, respectively, saidviscosifying copolymer characterized in that a 0.5% by weight aqueoussolution of said viscosifying copolymer has a viscosity of about 50,000to 300,000 cps at 1 RPM; andadding an effective amount of saidviscosifying copolymer to said water.
 11. The method of claim 10,wherein the carboxylic acid monomer comprises at least two monomersselected from the group consisting of acrylic acid, partiallyneutralized acrylic acid, and mixtures thereof, together with a C₈ - C30ester of methacrylic acid selected from the group consisting of laurylmethacrylate, stearyl methacrylate, and mixtures thereof.
 12. The methodof claim 9, wherein the initiator is a member selected from the groupconsisting of a peroxide initiator and a redox initiator.
 13. The methodof claim 12, wherein the initiator is a redox initiator.
 14. The methodof claim 13, wherein the redox initiator comprises a mixture of aperoxide and an azo compound.
 15. The method of claim 14, wherein theperoxide is dibenzoyl peroxide and the azo compound is 2,2'-azobis(2,4-dimethylpentanenitrile).
 16. The method of claim 13, wherein thecarboxylic acid monomer is an α, β unsaturated acid.
 17. The method ofclaim 12, wherein the initiator is a peroxide initiator.
 18. The methodof claim 17, wherein the peroxide initiator is selected from the groupconsisting of t-butylperoctoate, dibenzoylperoxide, and lauroylperoxide.
 19. The method of claim 16, wherein the acid is acrylic acid.20. The method of claim 9, wherein the silicone solvent is a memberselected from the group consisting of a cyclomethicone, a linearpolydimethylsiloxane, a polymethylalkyl siloxane and a polyfluoroalkylmethyl siloxane.
 21. The method of claim 9, wherein the silicone solventis a cyclomethicone.
 22. The method of claim 21, wherein thecyclomethicone is a member selected from the group consisting ofoctamethylcyclotetrasiloxane, decamethylcyclopentasiloxane,dodecamethylcyclohexasiloxane and mixtures thereof.
 23. The method ofclaim 20, wherein the silicone solvent is a linear polydimethylsiloxane.24. The method of claim 23, wherein the linear polydimethylsiloxane is amember selected from the group consisting of hexamethyl disiloxane,octamethyl trisiloxane, decamethyl tetrasiloxane, dodecamethylpentasiloxane, and mixtures thereof.
 25. The method of claim 9, whereinsaid water contains a dissolved metal salt.